Flue gas filter



R. C. ROE

FLUE GAS FILTER 2 Sheets-Shet 1 Filed March 9, 195a R. C. ROE

FLUE GAS FILTER Oct. 8, 1940.

Filed March 9, 1958 2 Sheets-Sheet 2 gwumvbcya dPWcJQ Patented as; a,auto y 2,210,936 l mm G S mu Ralph 0. Rue, Englewood, N. 1., assignor ofone-- half to Stephen W. Borden, Summit, N. J.

, Application March a, 1938, Serial No. 194,145

. y 2 Claims. (01. 1109-1651 This invention pertains to equipment forfiltering flue gases from steam boilers and to preheating air for thesame. a

One of the objects 0! the invention is to remove the fly ash fromthefluegas and to eifectively dispose of the same. Another object is to-provide relativelyinexpensive equipment for the purpose and equipmentwhich requires a comparatively small amount of powerfor its operation.An other object is to provide aunitary means for filtering the flue gasand for transferring heat from the flue gases to the air used forcombustion.

The drawings, which are schematic, represent a gas fine and anair-intake flue having a common partition and, these, together with afilter belt. are shown, partly in section, in Figs. 1,2, and Fig. 1 is asection 'on'line 3-3 of Fig. 3. Figs. 2 and 3 are each sections or viewspartly in section.

Fig. 4 is a schematic representation of a slag-tap furnace installedlina watertube boiler and having a filter of the type shown in Fig. Imounted I on top oftheboiler. I

The equipment mayconsist of an endless belt which passes first through achannel in which the flue gas is flowing andin such manner that the fluegasis forced to pass through the belt and immediately thereafter thebelt passes through a second channel where the belt is cleaned, thisbeingaccomplished in the case of slag tap furnaces. by means of thestream of incoming air which is used for combustion. The

belt is constructed of woven fabric, either with or without mechanicalreinforcing, consisting principallyof spun glass, rock wool, asbestosfiber or similar material whichis capable of withstanding hightemperatures and at the same time capable of being woven into a meshclose enough to act as a filtering medium and yet porous enough to allowpassage of gas and air through the same. I prefer woven glass fabric.

Referring to the drawings, Figs. 1, 2, and 3, l is a flue gas channel,having an exterior wall, I, in which theflue gases froma boilerflow'upward injthe direction indicated by the arrow, and I is anintakeair channel for the boiler, having an exterior wall 2, and in which airis flowing to [the boiler in the direction indicated by the arrow.

I6 is a common wall between thetwo channels.

I is the filter belt which is supported by rollers 8 revolving inbearings l0 and driven by a slow speed motor 8. '5 is a pressure plateinstalled above the belt, and Ms a pressure plate installed below thebelt. Fig. 2 ista view looking directly down into the channels, I beingthe pressure plate in the fluegas channel while the pressure plate 6 inthe air channel is beneath the belt i. I prefer to make the belt 1 ofwovenglass fabric but it may be 'of any woven fabric which is capable ofwithstanding the temperatures involved and having a sufllcientlyclosemesh to act as a fllter- 5 ing medium and yet porous enough to allowpassageof gas and air through the same. As the belt moves, slowly,through the flue gas duct 4, it accumulates, largely on thesurface, alarge amount of dust and ash contained in the flue gases which arepassing throughthis duct and hence through the belt. The pressure of thefiuegas against the belt is taken up by the stationary grid plate 5 uponwhich the belt slides. Passing through the common wall 16, the beltenters chamber 8 where it enters the stream of incoming air flowing tothe furnace, which air blows off the dust accumulated in passage 4, and

carries it back to the furnace" where it originated.

If the furnace is of the slag tap variety, 9. great w deal of this dustis melted and never reappears in the gases again although a smallportion of it i will. reappear and have to be againreturned'to thefurnace.

It will be noted that from channel i into channel ii and thereforewhatever heat is taken up by belt I from the flue gases is transferredto the combustibn airentering the furnace, and if belt i. is reinforcedwith metal members, either woven into the fabric or in the form ofsupporting frames, the amount of 3 heat thus transferred will besubstantial and this is a useful function of the device.

Referring nowto Fig. 4. Fuelfor the slagtap furnace enters through ducts60 and burners M 5!! into the hot zoneof the \furnace which is indicatedgenerally by the space 581. Primary air for combustion is drawn fromwindbox l9 and enters the combustion chamber with the fuel and secondary air may enter directly from box 4! into thecombustion chamber.From the combustion chamber the gases of combustion and somenoncombustible materials leave the chamber through passage if asindicated by the arrow and flow upward through boilerfl through thevarious tube banks, superheater II, economizer It and through the heatexchanger 45 and into the fluegas duct 4 and thence through filter beltI to the atmosphere. Air for combustion is drawn in through duct 3 andon its way to the furnace passes through the'belt I and heat exchanger45 to windbox 49, from whence part is introduced into thefurnace alongwith the fuel and part may go in directly.

In. the slag-tap type of furnace the maximum belt 1 passes immediatelytemperature in combustion chamber 8| runs between 3000" and 3200Fahrenheit and this high temperature is suflicient to melt practically!all noncombustible matter introduced into the furnace and it fallsdownward onto grate 61 where it-iorms a molten mass which is tapped ordrawn oflas desired. In this type of furnace, as differentiated fromother types, the only reason why ticle has been caught by the strongdraft and carried out of chamber 58; However, 11' these particles arerepea odly introduced into chamber 56 it is obvious thatthey willeventually be melted down or caught in the'rain of melted particles orbecome attached to melted particles by the flock action which exists insuch furnaces.

The non-combustible, consisting mostly or my ash, is collected from theoutgoing gas by the fliter and then conveyed into the stream of in,coming air I and therefore is carried back into combustion chamber 56.

The disposition o! the slag from a slag-tapfurnace is a comparativelysimple and inexpensive matter and in fact the cooled slag. which isglass hard, has some commercial value and therefore the cost ofdisposing of the same is very small and in fact sometimes represents aprofit. On the other hand, methods of disposing of fly ash, regardlessof the method employed for col- "iecting the flyash from the flue gas,have been expensive and by no means satisfactory; It will be clear thatmy arrangement not only filters the'flue gas and removes the fly ashtherefrom but? that it disposes of the fly ash in a less expensive andmore satisfactory manner than any method heretofore employed.

While I have described certain features more or less in detail, it willbe understood that the invention will employ various devices ofdiflering forms and construction and it is to be understood that theinvention is not to be limited except by the scope of the appendedclaims taken in conjunction with the state of the prior art. 1 What Iclaim is:

l. The combination with a coal-burning fur- I nace for operation at atemperature of 3000 degrees Fah. and higher and having a duct forconducting flue gases, containing fly ash and dust, away from thefurnace and a duct for conveying combustion air under pressure to thefurnace; of an endless woven fabric fllter belt positioned to pass firstthrough theflue gas duct, for filtering ash and dust from the flue gasand accumulating the same onthebelt, and thence through the combustionair duct for introducing the ash and dust'from the belt into the streamof combustion air at a-point between the filter and the furnace, andmeans for continuously driving the said endless belt.

2. The combination with a fuel burning furnace for operation atrelatively high temperatures and having a'duct for conducting fluegases, containing fly ash and dust, awayjrom the furnace and a duct forconveying combustion air under pressure to the furnace; of an endlessfilter belt positioned to pass first through the flue gas duct, forfiltering fly ash and dust from the flue gases and-accumulating the sameon the belt, and thence through the combustion air duct ior introducingthe ash and dust from the belt into the stream of combustion air at apoint between the filter and the furnace, and

means for continuously driving the said endless belt. l

RALPH C. ROE.

